1. Field of the Invention
The present invention generally relates to a tape cassette and, more particularly, is directed to a molding material of a cassette shell of a tape cassette.
2. Description of the Prior Art
FIG. 1 shows a plan view of an example of an arrangement of a cassette half or cassette shell in a conventional audio compact cassette.
In FIG. 1, a cassette shell, body 1 has a thick portion 2 which is shaped substantially as a trapezoid forming a front opening portion into which a magnetic transducer head (not shown) or the like is inserted, capstan insertion apertures 3a and 3b respectively, positioning apertures 4a and 4b respectively, a window portions which enables the user to visually confirm the state of a magnetic tape (not shown), and reel shaft insertion apertures 6a and 6b formed through the window portion 5, respectively.
In the thus arranged cassette shell, the cassette shell body 1 is made of an opaque resin of proper color and the window portion 5 is made of a transparent resin. Accordingly, the cassette shell body 1 and the window portion 5 are molded by a so-called dichromatic molding process in which the cassette shell body 1 is initially molded by an injection molding process, and then the window portion 5 is molded to be unitary with the cassette shell body 1 by an injection molding process.
In the conventional cassette shell molded by the dichromatic molding process, high impact polystyrene (HI-PS) is used as the opaque resin of the cassette shell body 1 and general purpose polystyrene (GP-PS) is used as the transparent resin of the window portion 5.
However, since high impact polystyrene utilized as the opaque resin of the conventional cassette shell body contains a high rubber component, such high impact polystyrene is low in rigidity as compared with general purpose polystyrene used as the transparent resin for the window portion. If the rigidity of the cassette shell is low as set forth above, then the cassette shell is easily affected by vibration when a magnetic tape is transported and a modulation noise of the magnetic tape is unavoidably increased. Further, the cassette shell made of high impact polystyrene is not uniformly glossy because of a relationship between the amount of rubber component and dispersion thereof, and it is therefore to be noted that the cassette shell body made of high impact polystyrene does not look excellent.